Field of the Invention
The present invention relates to a method of identifying the direction of rotation of a wheel using Hall probes which are disposed about the circumference of the wheel, via evaluation signals phase-shifted relative to one another.
In a large number of cases, it is desirable to detect not only the position and speed of a rotating wheel, for example a gearwheel, but also the direction of rotation of the wheel. In general, a sensor that is capable of establishing the position, speed and direction of rotation of a wheel is thus sought.
For detecting the position and speed of a gearwheel, there is already a differential dynamic Hall sensor which measures the difference field between two spatially offset Hall probes and gives especially good results if the phase angle between the two signals produced by the two Hall probes is 180.degree.. This is because, in this case, one Hall probe lies over a tooth of the gearwheel, while the other Hall probe lies over a gap between two teeth of the gearwheel. With such a differential dynamic Hall sensor, however, it is not possible to identify the direction of rotation of the gearwheel.
This is because in order to identify the direction of rotation of a gearwheel as well, yet another item of phase information is necessary, and this can be made available by two Hall sensors offset by 90.degree. relative to one another.
German Utility Model DE 89 09 677 U1 discloses a device for identifying rotation in which digital signal sequences are respectively derived from at least three Hall probes by at least two differential Hall ICs. For accurate rotational speed identification, with a view to higher resolution, the frequency of the output signal can be doubled relative to that of only one single differential Hall IC. By phase comparison, it is in principle also possible to identify the direction of rotation.
Published, Non-Prosecuted German Patent Application DE 41 04 902 A1 discloses a method and a configuration for identifying a direction of motion, in particular a direction of rotation. To that end, two signals, phase shifted by 90.degree., which are derived from two receivers disposed offset in the direction of motion of a signal source, are formed by adding and subtracting the output signals. From the sign of the 90.degree. phase shift between the sum and difference signals, the direction of rotation can be uniquely determined. This method is, however, highly sensitive to DC magnetic fields. There is therefore an offset in the sum signal relative to the difference signal, which is twice as great as the DC magnetic field, with the result that reliable further processing of these signals entails serious difficulties.